Tips for pouch cells

A user guide.

Watch out for one "feature" that ruined many of cells: the fused seams along sides are *conductive* and there is voltage potential between edges of the cell and its terminals. I found it hard way when put aluminum around thinking that plastic pouch the cell is in is insulator. Cells got discharged to zero when touched aluminum sinks. When I asked Kokam why they "withhold" such important design information on their web site (conductivity of the pouch) that resulted in ruining some cells in my case, they responded that basically one has to send them battery enclosure design for approval, else they are not responsible for such "omissions".

So insulate battery edges if you want to use them in conductive container! I've learned quite a bit assembling and testing these cells, and cutting open failed ones to see how they are made.

(Thanks to Victor Tikhonov of Metric Mind for the tip.)

The chemical components in Li-Ion cells expand as their State Of Charge increases. The cell may be damaged if this expansion is not contained (layer separation).

Pouch cells do not contain that expansion at all, and must be placed in a case.

If a pouch cell manufacturer tells you that containment is not required, run away from them: they don't know what they're doing.

The expansion of a stack of pouch cells is contained by:

• Placing hard plates on either side of the stack
• Squeezing the stack of cells with the plates as far as possible (use threaded rods and screw in the nuts as far as they go)
• Clamping the lot by keeping the threaded rods in place or with metal packing straps